Method for producing a porous carbon article and an article produced thereby

ABSTRACT

The present invention relates to a method for producing a porous carbon article comprising the steps of forming a workpiece with transport porosity and forming nanopores in said workpiece by thermochemical treatment. According to the invention the workpiece is formed as a rigid carbonaceous skeleton containing in its structure particles of one or more carbides, being selected and arranged in order to provide predetermined nanopore sizes, a predetermined volume of nanopores and a predetermined distribution of nanopores within the volume of the article.

TECHNICAL FIELD

[0001] The present invention relates to a method for producing a porouscarbon article comprising the steps of forming a workpiece withtransport porosity and forming nanopores in said workpiece bythermochemical treatment. The invention also relates to an articleproduced by said method.

BACKGROUND TO THE INVENTION

[0002] From “Application of tubular articles in cryoadsorptionpumps//Carbon adsorbents and their application in industries.”,Breslavets K. S et al, Moscow, Science publishers, 1983, p. 243, amethod for producing a porous carbon article is known. The methodcomprises a step of forming or extrusion of a paste consisting ofsilicon carbide powder and commercial synthetic resins as a binder inorder to produce a desired article. In this case, transport porosity ofthe material is formed with pore size above 100 nm. Then a carbonizationin an inert medium is carried out in order to strengthen the article andmake its structure more uniform. Further the article undergoes athermochemical treatment by chlorine at 900-1000° C. for transformationof carbide into carbon. In this step, in the volume of the article ananoporous structure with pore size less than 10 nm is formed.

[0003] Use of a polymeric resin as a binder is an obstacle for obtaininghigh mechanical strength, because of the low mechanical strength ofcarbonized resin. Resin destruction accompanies formation of carbonwhich also takes part in the process of forming nanoporosity, but thesize of this porosity is practically uncontrollable. As a result, it isimpossible to produce materials with predetermined adsorption propertieswith the known method.

[0004] An article produced by means of the known method is a carbonmaterial binded with products of resin carbonization with porosity of 65to 75 vol % in this case, a part of the pores, 30-32 vol % are transportpores having size greater than 100 nm, while other pores have size lessthan 10 nm.

[0005] Application of articles obtained by the known method isrestricted because it gives no possibility to obtain controllable sizeof pores as well as controllable volumetric content of both transportporosity and nanoporosity.

[0006] A number of so called activated carbons with a high content ofnanoporosity is known, but the pore size distribution for thesematerials is very wide and uncontrolled, c.f. “Carbon”, John Wiley &Son, N.Y. 1988,USA.

[0007] It is thus a need for a method in which the porosities of aporous carbon material which comprise two types of pores can becontrolled. The two types are pores of a size less than 10 nm providingadsorption ability and pores of a size greater than 100 nm providingtransportation of a component to the pores taking active part in theadsorption process. Articles produced by such a method can be used indifferent fields of technology connected with adsorption and absorptionprocesses, such as selective absorption of a component from a liquid orgas, electrochemical electrodes, in medicine technologies, etc.

[0008] The object of the present invention is to make it possible toproduce carbon porous articles with predetermined transport porosity andpredetermined nanopore sizes, volume and distribution throughout thevolume of the article.

SUMMARY OF THE INVENTION

[0009] This object is achieved by a method for producing a porous carbonarticle comprising the steps of formation of one or more carbide powdersto an intermediate body with transport pores, i.e. pores having a sizelarger than 100 nm, by shaping, characterised by the further steps of,selecting the one or more carbide powders on the basis of dependence ofspecified nanopore size on physical and chemical constants of thecarbides using the relationship;

X=Z*(1−R)/R

[0010] where

[0011] X=specified size of nanopores, nm;

[0012] Z=0.65-0.75 nm;

[0013] R=νM_(c)ρ_(k)/M_(k)ρ_(c)

[0014] where

[0015] M_(c)—molecular mass of carbon, g/mole;

[0016] M_(k)—molecular mass of carbide, g/mole;

[0017] ρ_(k)—density of carbide, g/ccm;

[0018] ρ_(c)—density of carbon, g/ccm;

[0019] ν—number of carbon atoms in carbide molecule,

[0020] heat treating the intermediate body in a medium of gaseoushydrocarbon or hydrocarbon mixtures at a temperature exceeding thedecomposition temperature for the hydrocarbon or hydrocarbons until themass of the intermediate body has increased at least 3% thereby creatinga workpiece in the form of a rigid carbonaceous skeleton,

[0021] thereafter thermochemically treating the work piece in a mediumof gaseous halogens

[0022] to provide predetermined nanopore sizes, i.e the pores have asize less than 10 nm, a predetermined volume of nanopores, and apredetermined distribution of nanopores within the volume of thearticle, the carbides used forming carbons having a slot-like structure.By this method materials having controlled and predetermined nanopores,an optimal ratio between volumes of transport pores and nanopores, highmechanical strength and complicated shapes can be produced.

[0023] In a preferred embodiment elements from III, IV, V or VI group ofMendeleyv's Periodic system are selected as carbon precursor.

[0024] The formulation of carbide particle mixture is chosen independence of desired distribution of nanopores by sizes using therelationship;

Ψ_(i)=K_(iφi)/ΣK_(iφi)

[0025] where

[0026] Ψ_(i)—volumetric part of nanopores with size x_(i) in totalvolume of nanopores;

[0027] φ_(i)—volumetric part of i-th carbide in particle mixture;

[0028] n—number of carbides;

K _(i)=1−νM _(c)ρ_(ki)/M_(ki)ρ_(c)

[0029] where

[0030] M_(c)—molecular mass of carbon, g/mole;

[0031] M_(ki)—molecular mass of it-h carbide, g/mole;

[0032] ρ_(ki)—density of it-h carbide, g/ccm;

[0033] ρ_(c)—density of carbon, g/ccm;

[0034] ν—number of carbon atoms in carbide molecule.

[0035] The intermediate body is formed with a porosity of 30-70 vol %,preferably 35-50 vol %, the porosity being determined with the followingrelationship;

ε₀=[1−ν_(np) /ΣK _(iφi)]*100

[0036] where

[0037] ε₀—porosity of intermediate body, vol %;

[0038] φ_(i)—volumetric part of i-th carbide in particle mixture;

[0039] ν_(np)—predetermined volumetric part of nanopores in finalarticle;

K _(i)=1−νM _(c)ρ_(ki) /M _(ki)ρ_(c)

[0040] where

[0041] M_(c)—molecular mass of carbon, g/mole;

[0042] M_(ki)—molecular mass of it-h carbide, g/mole;

[0043] ρ_(ki)—density of it-h carbide, g/ccm;

[0044] ρ_(c)—density of carbon, g/ccm;

[0045] ν—number of carbon atoms in carbide molecule.

[0046] The treatment in a medium of gaseous hydrocarbon or hydrocarbonis carried out until the mass of the intermediate body has changedaccording to the following relationship;

Δm=Q(ε₀ −v _(tr))/(1−ε₀)

[0047] where

[0048] Δm—relative change of intermediate body mass, g/g;

[0049] ε₀—porosity of intermediate body, vol %;

[0050] v_(tr)—predetermined volumetric content of transport pores, vol%;

Q=ρ _(c)/ρ_(mix)

[0051] Where ρ_(c)=density of carbon, g/ccm;

[0052] distributed uniformly or nonuniformly throughout the volume ofthe article.

BRIEF DESCRIPTION OF THE DRAWING

[0053] The present invention will now be described with reference to thefollowing figures, of which;

[0054]FIG. 1 shows a table of the properties of materials produced inexample 1, and

[0055] ρ_(mix)=density of carbides mixture, g/ccm;

[0056] The intermediate body can be formed by pressing. Other well knownforming methodes, such as slip casting, tape casting or slurry castingand injection moulding can of course also be used. nNatural gas is usedas a mixture of hydrocarbons and the treating in hydrocarbon medium iscarried out at 750-950° C.

[0057] Alternatively at least one of the hydrocarbons used during thetreatment of the intermediate body in hydrocarbons medium is selectedfrom the group of acetylene, methane, ethane, propane, pentane, hexane,benzene and their derivatives and the treating in hydrocarbon medium iscarried out at 550-1200° C.

[0058] The particles of carbide or carbides of which the intermediatebody is formed are arranged uniformly or nonuniformly throughout itsvolume.

[0059] The thermochemical treatment of the workpiece is carried out in amedium of gaseous halogens at 350-1200° C., preferably chlorine. at500-1100° C.

[0060] The present invention relates also to a porous carbon articlehaving nanopores, i.e pores having a size less than 10 nm, and transportpores, i.e. pores having a size grater than 100 nm, characterised inthat the article consists of a rigid carbon skeleton in which at least3% of its mass consists of carbon without nanopores.

[0061] In an embodiment the article has nanopores of at least two sizes.Furthermore, the volume of nanopores is 15-50% and the volume oftransport pores is 10-55% the nanopores are FIGS. 2-4 discloseporosimetry data for the sample of examples 1-4.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0062] The method according to the invention comprises the followingsteps:

[0063] 1) Forming a workpiece with transport porosity using particles ofa carbide or carbides of elements from III, IV, V and VI groups ofMendeleyev's Periodic System, in the form of a rigid carbonaceousskeleton containing in its structure particles of a carbide or carbidesselected from the said groups and arranged in a predetermined orderproviding formation in the subsequent steps desired transport porosityand nanoporosity by sizes, volume and distribution of pores throughoutthe volume of the article;

[0064] 2) Formation of nanoporosity throughout the volume of a workpieceobtained in the 1st step by thermochemical treatment of the saidworkpiece in gaseous halogens, such as chlorine, at elevatedtemperatures in the range of 350 to 1200° C., preferably 500-1100° C.

[0065] Current notions of carbon materials structure point out thatnanopores generated during the thermochemical treatment process areformed by ordered or disordered graphite planes of carbon, which forsimplicity might be considered as shaped as slots, the width of thelatter depending on type of carbide used for forming of the workpiecewith transport porosity.

[0066] These theoretical ideas are in good agreement with experimentaldata which allowed the inventors to disclose the following dependencefor carbon materials having such structure:

X=Z*(1−R)/R  (1)

[0067] where

[0068] X-predetermined size of nanopores, nm;

[0069] Z—experimental factor established for a number of carbidestructures of elements from III, IV, V and VI groups of Mendeleyev'sPeriodic System as 0.65-0.75 nm;

R=νM _(c)ρ_(k) /M _(k)ρ_(c)

[0070] where

[0071] M_(c)—molecular mass of carbon, g/mole;

[0072] M_(k)—molecular mass of carbide, g/mole;

[0073] ρ_(K)—density of carbide, g/ccm;

[0074] ρ_(c)—density of carbon, g/ccm;

[0075] ν—number of carbon atoms in carbide molecule.

[0076] A series of preliminary experiments made it possible to choose anecessary carbide to obtain in practice a predetermined size ofnanopores.

[0077] Particles of a chosen carbide (powder) are formed into anintermediate body with porosity in the range of 30-70 vol % by any knownmethod, e.g. by pressing with or without temporary binder, slip casting,slurry casting. Final step of forming, which results in production of aworkpiece with a high mechanical strength and a desired transportporosity, is a treating of the intermediate body in a medium of gaseoushydrocarbon or hydrocarbons mixture at a temperature above theirdecomposition temperature.

[0078] It is possible to use natural gas and/or at least a hydrocarbonselected from the group comprising acetylene, methane, ethane, propane,pentane, hexane, benzene and their derivatives.

[0079] Under these conditions a decomposition of hydrocarbon occurs byreaction;

C_(m)H_(n) →mC+^(n)/₂H₂↑  (2)

[0080] with deposition of the generated pyrocarbon on the surface and inthe pores of intermediate body volume.

[0081] The specified range of initial porosity is baser on the fact thatat a porosity below 30% it is difficult to obtain sufficient volume oftransport pores in the article providing access of adsorptive tonanopores where adsorption process occurs and at a porosity above 70%the article does not possess satisfactory mechanical strength.

[0082] The value of 35-50 vol % is preferable because it is easilyachieved by any available method of workpiece forming and it assures anoptimal relation between volumes of transport pores and nanopores in thearticle.

[0083] The size and distribution of the transport pores can becontrolled by selecting appropriate particle sizes and particledistribution. The amount of possible particle packing due to the formingprocess will of course also influence the porosity of the work piece.

[0084] Calculation of concrete value of intermediate body porositynecessary to obtain a predetermined volume of nanopores, is carried outusing the following expression: $\begin{matrix}{ɛ_{0} = {\left\lbrack {1 - {v_{np}/{\sum\limits_{i - 1}^{n}{K_{i}\phi_{i}}}}} \right\rbrack \cdot 100}} & (3)\end{matrix}$

[0085] where

[0086] ε₀—porosity of intermediate body, vol %;

[0087] φ_(i)—volumetric part of i-th carbide in powder mixture;

[0088] V_(np)—predetermined volumetric part of nanopores in finalarticle.

K _(i)=1−νM _(c)ρ_(ki) /M _(ki)ρ_(c)

[0089] where

[0090] M_(c)—molecular mass of carbon, g/mole;

[0091] M_(ki)—molecular mass of i-th carbide, g/mole;

[0092] ρ_(c)—density of carbon, g/ccm;

[0093] ρ_(ki)—density of i-th carbide, g/ccm:

[0094] ν—number of carbon atoms in carbide molecule;

[0095] n—number of carbides in the mixture.

[0096] Duration of treating in the said medium is controlled bymeasuring the mass of the article. When the mass has changed by at least3%, the strength is already sufficient for use of the article asadsorption element, capacitor electrode or chromatography membrane, forinstance.

[0097] The process is usually completed when the mass is changed by3-20%, thus providing necessary strength of the article and itstransport porosity. Lower and upper limits are determined by use ofcarbides from said groups with different densities.

[0098] In practice an experimental expression is used allowing for agiven type of carbide at predetermined strength properties to obtainnecessary value of transport porosity which, depending on active agentin the pores, can determine kinetics of the process. This expression isas follows:

Δm=Q(ε₀ −v _(tr))/(1−ε₀)  (4)

[0099] where

[0100] Δm−relative change of intermediate body mass, g/g;

[0101] ε₀—porosity of intermediate body, vol %;

[0102] V_(tr)—predetermined volumetric content of transport pores, vol%;

Q=ρ _(c)/ρ_(mix)

[0103] where

[0104] ρ_(c)—density of carbon, g/ccm:

[0105] ρ_(mix)—density of carbides mixture, g/ccm.

[0106] In order to obtain an article with nanopores of different sizes,making it possible to realize selective filtration and adsorption, morethan one carbide should be chosen. For this goal the formula (1) or anexperimentally determined pore size value is used and the followingdependence, confirmed experimentally, allows an determination of thepart of each carbide in the mixture necessary to manufacture such anarticle; $\begin{matrix}{\Psi_{i} = {K_{i}{\phi_{i}/{\sum\limits_{i = 1}^{n}{K_{i}\phi_{i}}}}}} & (5)\end{matrix}$

[0107] where

[0108] ψ_(i)—volumetric part of nanopores with size x_(i) in totalvolume of nanopores;

[0109] φ_(i)—volumetric part of i-th carbide in powder mixture;

[0110] n—number of carbides;

K_(i)=1−νM _(c)ρ_(ki) /M _(ki)ρ_(c)

[0111] where

[0112] M_(c)—molecular mass of carbon, g/mole;

[0113] M_(ki)—molecular mass of i-th carbide, g/mole;

[0114] ρ_(ki)—density of it-h carbide, g/ccm;

[0115] ρ_(c)—density of carbon, g/ccm;

[0116] ν—number of carbon atoms in carbide molecule.

[0117] In order to obtain a uniform distribution of nanopores throughoutthe article volume a mixture is formed with uniformly distributedpowders of various carbides in it (homogeneous mixture); if it isnecessary to obtain nanopores distributed throughout the volume in adesired order a mixture is prepared by means of any known method withparticles distributed according to the desired order, e.g. layerwise.

[0118] After completed forming, a workpiece is obtained as a rigidcarbonaceous skeleton with transport porosity formed in its volumeallowing to obtain in the step of thermochemical treatment uniformnanopores of a predetermined size.

[0119] In order to form nanoporosity the obtained workpiece is subjectedto thermochemnical treatment by chlorine at 500-1100° C. Nanoporosity isformed at removal of volatile chlorides of carbide-forming elements inaccordance with reaction:

E _(k)C_(f)+(km/2n)Cl₂ →k/nE _(n)Cl_(m) ↑+fC  (6)

[0120] where

[0121] E_(k)C_(f)—primary carbide;

[0122] k, f, n, m—stoichiometric coefficients.

[0123] The treatment is carried out until mass change of the workpiecehas stopped.

[0124] A finished article produced by the described method has apredetermined shape and size, and its structure is a porous carbonskeleton with transport porosity of 10-55% obtained in the step offorming and nanoporosity of 15-50% volume. The article comprises one orseveral types of nanopores and each type is being characterized withnarrow distribution by size. Carbon content in the skeleton is more than95 wt %, preferably 99 wt %, i.e., practically, the obtained articleconsists of pure carbon and has considerable strength allowing toincrease its life time and expand application range under conditionswhen shape maintaining during operation is necessary.

[0125] As a result of selecting appropriate carbides and accomplishmentof forming under conditions determined beforehand by means ofrelationships established by the inventors, a finished article isobtained with nanopore sizes, volume and distribution corresponding tothose of the object of the article operation.

[0126] Among possible forming methods to realize the said methodpressing, slip casting, tape casting and slurry casting can be named.

[0127] A formed intermediate body is treated in a medium of at least onehydrocarbon selected from the group comprising acetylene, methane,ethane, propane, pentane, hexane, benzene and their derivatives. Whenusing hydrocarbons from the said group an optimal temperature range is550-1200° C., the decomposition temperatures for these hydrocarbonsfalling within this range. It is also possible to use natural gas and inthis case it is expedient to keep temperature in the range of 750-950°C.

[0128] A halogenation is carried out just like in the known method, withthe temperature being selected in the range of 350-1200° C., dependingon the nature of initial carbides and the formed volatile halogenides.Under these conditions volatile halogenides of carbide-forming elementsare completely removed out of the article according to a reactionsimilar to reaction (6). However, only halogens and halogenides which donot react with carbon under the prevailing temperature conditions may beused.

[0129] The claimed concept is further elucidated with the followingexamples.

EXAMPLE 1

[0130] An example of producing an article in the tablet form with sizesd=20 mm, h=5 mm, with nanopore size 0.8 nm and nanopore volume 0.3ccm/ccm uniformly distributed throughout the article volume, suitablefor forming on its surface a double electric layer of high capacitancein electrolyte solutions.

[0131] To produce an article on the basis of beforehand obtaineddependence (1) for X=0.8 nm titanium carbide powder was chosen. Bysubstitution of the values of molecular mass and density of titaniumcarbide and carbon (M_(c)=12 g/mole; ρ_(c)=2.2 g/ccm; ρ_(k)=ρ_(TiC)=4.92g/ccm; M_(k)=M_(TiC)=59.88 g/mole) in the formula (1) the following isobtained:

[0132] R=12*4.92/59.88*2.2=0.448, X=Z(1−0.448)/0.448=1.232Z nm;

[0133] Thus when Z is in the range of 0.65-0.75, the nanpore size of theproduced carbon materials will be in the range of 0.8-0.92.

[0134] In order to obtain the predetermined volume of nanopores(V_(np)=0.3 ccm/ccm), prior to pressing a needed porosity of theintermediate body is determined by the relationship (3): where φ_(i)=1,n=1, as follows

ε₀=[1−0.3/(1−0.448)]*100=46%

[0135] Amount of TiC powder necessary to produce an intermediate bodywhich has the predetermined sizes and the obtained value of porosity iscalculated by the following dependence:

m=ρ _(k)(100−ε₀)·V/100

[0136] where

[0137] V—article volume, V=(πd²/4)*h, ccm;

[0138] d—workpiece diameter, 2 cm;

[0139] h—workpiece height, 0.5 cm; hence:

[0140] m=4.92(100−46)(3.14*2^(2/)4)*0.5=5.01 g

[0141] The needed mass change of the workpiece during pyrocarbondeposition is calculated by formula (4), assuming a transport porosityof 35 vol %

[0142] Then, Δm=[0.4476(46−35)/(100−46]*100=9.1%

[0143] A mixture is prepared using 5.01 g of TiC powder with a size ofthe particles of 20 μm. Ethyl alcohol is added in the amount of 10%, ofthe mass of the mixture. Then, an intermediate body is formed bypressing on a hydrostatic press machine (P-125) at 30±1 Mpa pressure.After the pressing, the intermediate body is dried at 150±10° C. during1-1.5 hour until complete removal of temporary binder.

[0144] This is followed by pyrocarbon deposition on the workpiece bymeans of heat treatment in natural gas medium at atmospheric pressure ina quartz continuous reactor at 850° C. during 12 hours until change ofmass by 9.1%.

[0145] Then, the sample is chlorinated. The chlorination is carried outin a isothermal quartz reactor at 650° C. during 4 hours. Then ablow-through of the reactor with argon at a temperature of 800° C. iscarried out to remove excessive chlorine out of the reactor zone and theinternal surface of the sample.

[0146] Properties of the obtained material are presented in Table 1.From this table it is evident that the measured peak value of thenanopore size measured by gas porosimetry correspond to the calculatedvalue.

[0147] Two articles produced according to Example 1 were saturated with20% KOH solution by boiling and placing them in an electrolyte solution(20% KOH). Opposite by sign potential was applied to each of thearticles to form a double electric layer in the material nanoporevolume. In this case the specific electrical capacitance of the doubleelectric layer formed in the material was 37.8 F/g.

EXAMPLE 2

[0148] The example of producing an article in a tablet form of d=30 mm,h=3 mm with a nanopore volume 0.4 ccm/ccm uniformly distributedthroughout the article volume suitable for adsorption of organicsubstances out of a powder of Mo₂C was chosen.

[0149] In order to produce the predetermined nanopore volume (v_(np)=0.4ccm/ccm) before pressing the needed porosity of the intermediate bodywas calculated using expression (3), where M_(Mo2C)=203,88 g/mole;ρ_(Mo2C)=8.91 g/ccm, R=0.238; φ₁=1, n=1, as follows: ε₀=48%

[0150] The amount of molybden carbide powder necessary to produce theintermediate body having the predetermined porosity was calculated as inExample 1. In this case the powder article weight was calculated to:m=9.82 g

[0151] The needed mass change of the workpiece during pyrocarbondeposition was calculated by formula (4), assuming a transport porosityof 40 vol %, to Δm=3.8%.

[0152] Mixture preparation pyrocarbon deposition and chlorination werecarried out as in Example 1.

[0153] Properties of the obtained material are presented in Table 1.From this table it is evident that the calculated nanopore size of1.95-2.25 nm differs from the measured peak value according to FIGS. 3and 4 which was 3.5 nm. This indicates that Mo₂C probably does notfollow the model structure for dependence (1).

[0154] The produced article was placed in an exsiccator containingisooctane vapours and was kept there during 24 hours. Then, the articlewas weighed to determine the amount of adsorbed isooctane, which was0.95 ccm/g.

EXAMPLE 3

[0155] An example of producing an article of diameter 30 mm and height 5mm with nanopores of calculated size 0.8 nm and 2.1 nm uniformlydistributed throughout the article volume. In order to obtain thearticle on the basis of beforehand obtained dependence (1) for X₁=0.8 nmtitanium carbide powder was chosen, for X₂=3.5 nm—molybdenum carbidepowder in accordance with the measured value in Example 2.

[0156] In order to provide equal volumetric content of both sizesnanopores a mixture is used containing 40 vol % molybdenum carbide and60 vol % titanium carbide, that is determined by formula (5). The neededamount of these carbides is calculated as follows:

ρ_(mix)=φ₁·ρ₁+φ₂·ρ₂

[0157] where

[0158] φ₁, φ₂—volumetric content of titanium carbide and molybdenumcarbide, correspondingly φ₁=0.4, φ₂=0.6);

[0159] ρ₁, ρ₂—density of titanium carbide and molybdenum carbide,correspondingly (ρ₁=8.91 g/ccm, ρ₂=4.92 g/ccm);

[0160] hence ρ_(mix)0.4·8.91+0.6·4.92=6.52 g/ccm,

[0161] hence mass part of molybdenum carbide:

α₁=0.4*8.91/6.52=0.55 wt.fraction;

[0162] of titanium carbide

α₂0.6*4.92/6.52=0.45 wt.fraction

[0163] The mixture is prepared and pressed under conditions of Example1.

[0164] In order to obtain an article of the specified shape and sizes aweight should be calculated according to the following dependence:

m=ρ _(mix)(100−ε₀)*V/100

[0165] where

[0166] ρ_(mix)—density of carbide mixture;

[0167] ε₀—porosity of intermediate body; % vol;

[0168] V—article volume, ccm;

[0169] d—article diameter, 3 cm;

[0170] h—article height, 0.5 cm.

[0171] The needed porosity of an intermediate body is chosen accordingto relation (3).

[0172] By substitution of the said values at specified total volume ofnanopores 0.4 ccm/ccm we obtain

ε₀=[100−0.4/[(1−12*8.91/2.2*203.88)0.4+(1−12*4.92/2.2*59.88)0.6]100≈37vol %

[0173] hence necessary mass of the weight:

m=6.52(100−37)(3,14*5²/4)*0.2/100=16.1 g

[0174] The obtained intermediate body is heat treated under conditionsof Example 1. Introduction of pyrocarbon is carried out under conditionsof Example 1 until change of article mass by 7% which is determined byformula (4) under condition:

V_(tr)=20 vol %

Δm=0.337(37−20)/(100−37)*100=9.1%

[0175] Chlorination of the obtained workpiece is carried out underconditions of Example 1.

[0176] Properties of samples produced in Examples 1-3 are presented inTable 1. From Table 1 it seems as MO₂C results in a different carbonnanopore structure than TiC.

[0177] The produced article was placed in an exsiccator containingvapours of carbontetrachloride and was kept there during 24 hours. Thenthe article was weighed to determine the amount of absorbedcarbontetrachloride which was 0.61 ccm/g.

[0178] Notes:

[0179] 1) Total volume of pores is determined by hydrostatic methodaccording to GOST 473.4-81.

[0180] 2) Nanopore volume is determined by exsiccator method byadsorption of benzene under static conditions, see “Fundamentals ofadsorption technology.” Keltsev N. V., Moscow, Chemistry publishers,1984, p. 33.

[0181] 3) Transport pore volume is determined by formula

V _(tr) =V _(Σ) −V _(np).

[0182] 4) Size of nanopores is determined by means of mercery and gasporosimetry (Micromeretics Auto Pore III and Micromeretics ASAP 2010,respectively). Data are shown in FIGS. 2-4. Legend Hg denotes mercuryporosimetry intrusion data, legend BJH denotes gas porosimetrydesorption data analysed by the BJH method, and legend Micro denotes gasporosimetry data analysed by the Horvath-Kawazoe method.

[0183] The presented data allows one to draw the conclusion that a newmethod for producing a porous carbon article comprising transport poresand nanopores with controllable sizes and distribution of nanoporesthroughout its volume as well as volumetric content of both types ofporosity has been developed. The articles according to the invention canfind wide application for adsorption and microdosage of substances,purification and separation of cryogenic liquids and gas mixtures, ashigh-porous electrode materials etc. owing to presence of porosity ofdesired sizes.

[0184] By the inventive method it is possible to produce nanopore volumeand size or sizes by a mechanism independent from the mechanism forproducing transport porosity in the materials produced, thereby makingit possible to control purposely parameters of their porous structure.At development of adsorption materials, for instance, the followingparameters can be optimized when using the present invention:

[0185] 1) adaptability to manufacture of devices working components madeof these materials;

[0186] 2) optimal relationship between volumes of transport pores andnanopores which provide effective adsorption;

[0187] 3) mechanical strength;

[0188] 4) increased heat conductivity allowing to use these materials incryo-adsorption evacuation elements.

[0189] Furthermore, the present method, besides the advantages pointedout, allows production of articles of complex shapes, in particular, ofshapes impossible to obtain by any other known method, with minimummachining required. Owing to high mechanical strength the articlesaccording to the invention can be used under conditions demandingmaintenance of their shape.

1. A method for producing a porous carbon article comprising the stepsof formation of one or more carbide powders to an intermediate body withtransport pores, i.e. pores having a size larger than 100 nm, byshaping, characterised by the further steps of, selecting the one ormore carbide powdes on the basis of dependence of specified nanoporesize on physical and chemical constants of the carbides using therelationship; X=Z*(1−R)/R where X=specified size of nanopores, nm;Z=0.65-0.75 nm; R=νM_(c)ρ_(k)/M_(k)ρ_(c) where M_(c)—molecular mass ofcarbon, g/mole; M_(k)—molecular mass of carbide, g/mole; ρ_(k)—densityof carbide, g/ccm; ρ_(c)—density of carbon, g/ccm; ν—number of carbonatoms in carbide molecule, heat treating the intermediate body in amedium of gaseous hydrocarbon or hydrocarbon mixtures at a temperatureexceeding the decomposition temperature for the hydrocarbon orhydrocarbons until the mass of the intermediate body has increased atleast 3% thereby creating a workpiece in the form of a rigidcarbonaceous skeleton, thereafter thermochemically treating the workpiece in a medium of gaseous halogens to provide predetermined nanoporesizes, i.e the pores have a size less than 10 nm, a predetermined volumeof nanopores, and a predetermined distribution of nanopores within thevolume of the article, the carbides used forming carbons having aslot-like structure
 2. A method according to claim 1, characterised inthat elements from III, IV, V or VI group of Mendeleyv's Periodic systemare selected as carbon precursor.
 3. A method according to claims 1 or2, characterised in that the formulation of carbide particle mixture ischosen in dependence of desired distribution of nanopores by sizes usingthe relationship; Ψ_(i) =K _(iφi) /ΣK _(iφi) where Ψ_(i)—volumetric partof nanopores with size x_(i) in total volume of nanopores;φ_(i)—volumetric part of i-th carbide in particle mixture; n—number ofcarbides; K _(i)=1−νM _(c)ρ_(ki) /M _(ki)ρ_(c) where M_(c)—molecularmass of carbon, g/mole; M_(ki)—molecular mass of it-h carbide, g/mole;ρ_(ki)—density of it-h carbide, g/ccm; ρ_(c)—density of carbon, g/ccm;ν—number of carbon atoms in carbide molecule.
 4. A method according toany one of claims 1-3, characterised in that the intermediate body isformed with a porosity of 30-70 vol %, preferably 35-50 vol %.
 5. Amethod according to any one of claims 1-4, characterised in that theintermediate body is formed with a porosity determined with thefollowing relationship; ε₀=[1−ν_(np) /ΣK _(iφi)]*100 where ε₀—porosityof intermediate body, vol %; φ_(i)—volumetric part of i-th carbide inparticle mixture; ν_(np)—predetermined volumetric part of nanopores infinal article; K _(i)=1−νM _(c)ρ_(ki) /M _(ki)ρ_(c) whereM_(c)—molecular mass of carbon, g/mole; M_(ki)—molecular mass of it-hcarbide, g/mole; ρ_(ki)—density of it-h carbide, g/ccm; ρ_(c)—density ofcarbon, g/ccm; ν—number of carbon atoms in carbide molecule.
 6. A methodaccording to any one of claims 1-5, characterised in that the treatmentin a medium of gaseous hydrocarbon or hydrocarbon is carried out untilthe mass of the intermediate body has changed according to the followingrelationship; Δm=Q(ε₀ −v _(tr)/(1−ε₀) where Δm—relative change ofintermediate body mass, g/g; ε₀—porosity of intermediate body, vol %;v_(tr)—predetermined volumetric content of transport pores, vol %; Q=ρ_(c)/ρ_(mix) Where ρ_(c)=density of carbon, g/ccm; ρ_(mix)=density ofcarbides mixture, g/ccm;
 7. A method according to any one of claims 1-6,characterised in that the intermediate body is formed by pressing.
 8. Amethod according to any one of claims 1-6, characterised in that theintermediate body is formed by slip casting, tape casting or slurrycasting.
 9. A method according to any one of claims 1-8, characterisedin that natural gas is used as a mixture of hydrocarbons.
 10. A methodaccording to claim 9, characterised in that the treating in hydrocarbonmedium is carried out at 750-950° C.
 11. A method according to any oneof claims 1-8, characterised in that at least one of the hydrocarbonsused during the treatment of the intermediate body in hydrocarbonsmedium is selected from the group of acetylene, methane, ethane,propane, pentane, hexane, benzene and their derivatives.
 12. A methodaccording to claim 11, characterised in that the treating in hydrocarbonmedium is carried out at 550-1200° C.
 13. A method according to any oneof claims 1-12, characterised in that the particles of carbide orcarbides of which the intermediate body is formed are arranged uniformlythroughout its volume.
 14. A method according to any one of claims 1-12,characterised in that the particles of carbide or carbides of which theintermediate body is formed are arranged non-uniformly throughout itsvolume.
 15. A method according to any one of claims 1-14, characterisedin that the thermochemical treatment of the workpiece is carried out ina medium of gaseous halogens, such as chlorine.
 16. A method accordingto any one of claims 1-15, characterised in that the thermochemicaltreatment of the workpiece is carried out at 350-1200° C.
 17. A methodaccording to claim 15 or 16, characterised in that chlorine ispreferably used for the thermochemical treatment at 500-1100° C.
 18. Aporous carbon article having nanopores, i.e pores having a size lessthan 10 nm, and transport pores, i.e. pores having a size grater than100 nm, characterised in that the article consists of a rigid carbonskeleton in which at least 3% of its mass consists of carbon withoutnanopores.
 19. A porous carbon article according to claim 18,characterised in that it has nanopores of at least two sizes.
 20. Anarticle according to claim 18 or 19, characterised in that the thevolume of nanopores is 15-50% and the volume of transport pores is10-55%
 21. An article according to claims 18, 19 or 20, characterised inthat the nanopores are distributed uniformly throughout the volume ofthe article.
 22. An article according to claims 18, 19 or 20,characterised in that the nanopores are distributed nonuniformlythroughout the volume of the article.
 23. An article according to anyclaims 18-22, characterised in having a specific electrical capacitanceof at least 30 F/g when used as electrode material in a double electriclayer capacitor.